The present invention pertains generally to medical devices and more particularly to implantable medical devices such as devices for monitoring activity of the heart and providing electrical shock therapy thereto including automatic implantable cardioverter defibrillator devices for treating atrial arrhythmias and external patient operable devices for controlling the operation of such implantable medical devices.
Various types of medical devices are employed to monitor electrical or other activity of the heart and to provide therapy to the heart in response to the detection of irregular cardiac rhythms. Such devices may be implantable beneath the skin of a patient, i.e., in the patient""s chest. Such implantable devices include a hermetically sealed canister containing electronic circuitry for implementing the functions of the device, one or more electrodes implanted in one or more of the chambers of the heart, or in close proximity thereto, and leads for connecting the electrodes to the circuitry within the device canister. The device circuitry includes circuitry for detecting electrical signals produced by the heart, which signals are picked up at the electrodes, along with circuitry, typically implemented in a microprocessor, for analyzing the thus-detected cardiac signals. The device may also include circuitry for providing therapy in the form of electric shock signals applied to the heart. Such signals are provided to the heart, via the leads and electrodes mounted in the heart, in response to the detection of an irregular cardiac rhythm by the analysis circuitry based on the detected cardiac activity signals. The implantable device may also include a transmitter/receiver, for transmitting cardiac activity and other information to an external device for, e.g., storage and/or further analysis, and for receiving information, such as programming instructions, from the external device via, for example, an RF link.
An example of such an implantable cardiac device is an automatic implantable cardioverter defibrillator (AICD) for treating atrial arrhythmias, e.g., atrial tachycardia, fibrillation, flutter, etc. (The functionality of an atrial AICD may be combined with those of a bradycardia pacemaker, ventricular defibrillator, etc., in a single implantable device.) Atrial arrhythmias are probably the most common cardiac arrhythmia. Although atrial arrhythmias are not usually life-threatening, patients with atrial arrhythmias generally experience palpitations of the heart, and may experience dizziness or even loss of consciousness. Atrial arrhythmias, such as atrial fibrillation, also have been associated with strokes and other conditions. Atrial arrhythmias can occur suddenly. Implantable atrial cardioverter defibrillators are programmed to detect the onset of atrial arrhythmias and to provide an appropriate electrical shock therapy to the atria to terminate the atrial arrhythmia. The atrial shock therapy to be provided may depend upon the type of atrial arrhythmia detected, e.g., atrial tachycardia versus atrial fibrillation. Shock therapy provided by an implantable atrial cardioverter defibrillator may include a relatively high voltage level atrial defibrillation or cardioversion pulse, which is typically delivered to the atria in synchronism with a detected or paced ventricular activation, to terminate atrial fibrillation or flutter. Atrial antitachycardia pacing may be applied by the implantable device to terminate atrial tachycardia. Atrial antitachycardia pacing typically involves a train of pacing pulses applied to the atria at a rate slightly higher than the rate of the tachycardia.
Various systems and methods have been developed to allow patients having implanted atrial cardioverter defibrillators to monitor and control, to at least some degree, operation of the implanted device. For example, U.S. Pat. No. 5,490,862 describes an implantable atrial defibrillator which may be programmed to operate in a patient activated mode of operation. In the patient activated mode, an atrial fibrillation intervention sequence is performed by the implanted device in response to the receipt of a sequence command generated from external to the patient. The sequence command may be generated, for example, by an external magnet applied by the patient to near the implantation site, to close and then open a reed switch mounted in the implanted device and coupled to the device microprocessor. The intervention sequence thus initiated by the patient, when he believes he is experiencing an atrial arrhythmia, includes atrial fibrillation detection by the implanted device and, if atrial fibrillation is confirmed, the application of cardioverting electrical energy to the atria.
U.S. Pat. No. 5,674,249 describes the use of a portable communication device which allows a patient to monitor and control the operation of an implanted atrial defibrillator. The portable communication device, which may be dimensioned to be hand held by a patient, includes a transmitter/receiver for communicating with the implanted device via a telemetry (e.g., RF) link. In this system, an atrial fibrillation intervention sequence may be initiated in an implanted device in response to a sequence command generated from the portable communication device. The patient may also use the portable communication device to program the implanted device into an automatic mode, wherein the intervention sequence is initiated automatically at predetermined times. The handheld portable communication device receives an acknowledgment signal from the implanted device when a command signal sent from the communication device is received by the implanted device. The receipt of the acknowledgment signal by the portable handheld communication device is displayed to the patient on the device. The display includes a description of the task being performed by the implanted device in response to the command signal sent by the patient. Thus, a patient is able both to monitor and control operation of an implanted cardiac device to some degree.
U.S. Pat. No. 5,999,851 describes an implantable atrial defibrillator which includes an atrial fibrillation detection only mode of operation. In this mode, atrial fibrillation detection is initiated in the implanted device by a command signal sent from an external patient operated communication device, which is in communication with the implanted defibrillator via a telemetry (e.g., RF) link. If atrial fibrillation is detected by the implanted atrial defibrillator, an appropriate signal is communicated to the patient operated communication device, and a visual and/or audible message is provided by the communication device to the patient to indicate whether or not atrial fibrillation is detected. In this detection only mode, a further signal must be provided from the communication device to the implanted device to initiate cardioversion therapy, preferably after continued atrial fibrillation is confirmed by the implanted device.
In each of the systems described above, atrial fibrillation detection, or atrial fibrillation detection followed by atrial shock therapy, if required, may be initiated by a patient using an external communication device. In each case, where atrial shock therapy is requested by the patient, shock therapy is delivered by the implanted device immediately after it is requested by the patient (perhaps after a slight delay to confirm the presence of an atrial arrhythmia and to synchronize the atrial shock therapy delivery to a ventricular activation). The delivery of shock therapy to a patient""s heart can cause great discomfort to the patient. If shock therapy is delivered essentially immediately following a patient""s request, the patient""s ability to prepare for the therapy or to mitigate the discomfort of the therapy before therapy delivery is severely limited. For example, a patient may wish to take analgesics or a sedative, lie down, or take other measures, such as begin exercises (calisthenics), or go to sleep, to mitigate shock perception before atrial shock therapy is provided by an implanted device. Current systems, in which patient requested atrial shock therapy is provided essentially immediately following a therapy request, do not allow patients to make many of these preparations. It would be difficult for a patient to simultaneously exercise and request atrial shock therapy using a conventional system for patient requested shock therapy, if the patient wished to reduce shock perception using exercise. Similarly, it would be impossible for a patient to go to sleep and then initiate an atrial shock therapy request using a conventional system.
What is desired, therefore, is a system which allows a patient to control the providing of atrial shock therapy by an implanted device and in which the providing of therapy is delayed by a specific delay period after shock therapy is requested. The therapy delay period is preferably long enough for the patient to prepare for the application of shock therapy (e.g., by exercise, sleep, etc.) after a shock therapy request is made. Preferably, a patient is also able to adjust the therapy delay period and select whether shock therapy will be provided immediately upon request or after expiration of the delay period.
The present invention provides a system and method which allows a patient with an implanted automatic implantable cardioverter defibrillator to delay the providing of shock therapy to the atria by the implanted device in response to a patient request for shock therapy. In accordance with the present invention, a patient employs an external activator communication device to request therapy from an implanted device. A shock therapy delay period is timed by the implanted device in response to the patient therapy request. An appropriate atrial shock therapy is provided by the implanted device after expiration of the shock therapy delay period (preferably after confirmation of an ongoing atrial arrhythmia). The patient may be allowed to select the therapy delay period, and/or to select whether patient requested atrial shock therapy is provided by the implanted device immediately following a therapy request or after expiration of the shock therapy delay period.
The present invention may be implemented in an implantable cardiac device, such as an automatic implantable cardioverter defibrillator, which provides atrial arrhythmia detection and electrical shock therapy to the atria to terminate such atrial arrhythmias. (The implantable device may also provide ventricular arrhythmia monitoring and ventricular shock therapy functionality and/or ventricular pacing functionality, as well as atrial pacing capability.) The implantable cardiac device includes signal detection circuitry, connected via leads to electrodes positioned in the atria and, preferably, the ventricles of the heart, to detect electrical heart activity signals. An implanted device system processor monitors the output provided by the signal detection circuitry to detect the occurrence of an atrial arrhythmia, e.g., atrial tachycardia, fibrillation, and/or flutter, using known atrial arrhythmia detection algorithms. The implantable device includes cardioverter/defibrillator circuitry, controlled by the device processor, for providing defibrillation shock therapy, and/or antitachycardia pacing, depending upon the type of atrial arrhythmia identified, to the atria via the leads and electrodes implanted in the heart. The implantable device is preferably also provided with a telemetry receiver/transmitter, coupled to the device processor, to allow the processor to transmit cardiac activity and other data to an external programmer device for storage and/or further analysis, and to receive data, such as programming instructions, from the external programmer device. (The external programmer device is a relatively complicated device used by a physician to program the implanted device and query cardiac activity data therefrom.)
In accordance with the present invention, a patient, having an implanted cardiac device in accordance with the present invention, is able to control the providing of atrial shock therapy by the implanted device using a patient activator communication device. The patient activator is preferably a relatively small, handheld device, which allows the patient to send a patient therapy request to the implanted device to control the providing of shock therapy to the atria by the implanted device to terminate an atrial arrhythmia event The patient activator preferably employs a relatively simple mechanism for providing a patient therapy request. For example, the patient activator may include a magnet which, when placed near the implantation site of the implanted device, operates a reed switch in the implanted device, which is coupled to the implanted device processor, thereby to provide a patient therapy request to the implanted device.
In response to the receipt of a patient therapy request, the implanted device begins timing a shock therapy delay time period. The shock therapy delay time period may be pre-programmed by a physician, using an external programmer device, or programmed by the patient using a more sophisticated patient activator device. The delay time period is preferably selected to be sufficiently long so as to allow a patient sufficient time to prepare for and/or mitigate the discomfort of atrial shock therapy to be delivered to the patient in response to the atrial shock therapy request. The shock therapy delay time period may thus be set from several minutes (to allow a patient time to take an analgesic or sedative, to lie down, or to begin exercising) to several hours (to allow a patient to go to sleep after requesting therapy so that shock therapy is provided at night during sleep). After the shock therapy delay time period has expired, an appropriate atrial shock therapy is provided by the implanted device. Preferably, such atrial shock therapy is provided only after confirmation by the implanted device of an ongoing atrial arrhythmia event.
The patient activator communication device may also be employed to control an implanted cardiac device to withhold completely the providing of atrial shock therapy by the device. For example, a patient therapy request may only be detected by the implanted device if a patient therapy request signal is maintained for longer than a therapy request signal threshold duration, e.g., by maintaining a patient activator device magnet in position to operate the reed switch in the implanted device for more than the threshold duration. In such a case, the delay time period may be timed in response to removal of the patient therapy request signal (e.g., removal of the patient activator from the implant site) and an appropriate shock therapy (e.g., synchronized cardioversion and/or antitachycardia pacing, depending upon the nature of the atrial arrhythmia) provided by the implanted device after expiration of the delay time period and confirmation of an ongoing atrial arrhythmia. If the patient activator device is removed from near the implantation site shortly after it is applied (i.e., within less than the therapy request signal threshold duration from initial application of the activator to the implantation site), atrial shock therapy will be withheld (i.e., disabled), and no atrial shock therapy will be provided even though an atrial arrhythmia has been detected and atrial shock therapy is otherwise available. If the providing of atrial shock therapy is withheld in this manner, the patient may use the activator communication device to initiate delayed patient requested atrial shock therapy at a later time which is more convenient or appropriate for the patient.
Although a relatively simple and inexpensive patient activator device, e.g., including a magnet, may be employed in accordance with the present invention, a more complicated patient activator may also be used. A more complicated patient activator communication device may include a receiver/transmitter for communicating control signals to the implanted cardiac device via a telemetry (e.g., RF) link with a corresponding receiver/transmitter in the implanted device. Such a patient activator communication device may include a patient input circuit, including buttons, switches, etc., for allowing a patient to signal via the telemetry link from the activator to the implanted device a patient therapy request. A patient may employ such a patient activator communication device to provide different types of therapy requests to the implanted device to request either immediate atrial shock therapy, or delayed shock therapy, as described above. For example, using such an activator device, a patient therapy delay request may be provided by the patient to the implanted device. In response to receipt of the patient therapy delay request, shock therapy is provided by the implanted device after timing a shock therapy delay period (after the delay period expires and an ongoing atrial arrhythmia is confirmed). In contrast, atrial shock therapy may be provided to the patient by the implanted device immediately following receipt of a patient therapy request from the activator in which no therapy delay is requested. Such a patient activator may also be employed by the patient to provide a shock therapy delay period setting command to the implanted device, thereby to set the shock therapy delay period to a time period desired by the patient.
Further objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.